In general, SIBS techniques can be used to detect and quantitatively measure concentrations of elements in a given material of interest. These measurements can be accomplished, for example, by detecting spectral signatures of atomic emissions in a given material of interest. For example, the given material of interest may comprise heavy metals (such as lead, mercury, chromium, cadmium, arsenic, antimony and beryllium), alkali metals (such as lithium, potassium, rubidium, cesium and francium), radioactive materials (such as uranium, plutonium, thorium and technetium) or other materials of interest. In operation, a relatively powerful electrical spark discharge creates a small volume of hot plasma in which aerosol and solid particulates are quickly vaporized and components are reduced to atomic form. Initially, the plasma emits broadband, essentially continuous radiation. Monitoring of atomic emissions in selected wavelength bands during the relatively short period of time during which the plasma cools enables measurement of elemental concentrations.
One characteristic of current SIBS devices is that the initial plasma is created at a high temperature (e.g., from about a few thousand degrees to 10,000 degrees Celsius). These temperatures result in a high degree of ionization and subsequent recombination that creates a great deal of broadband background (Bremsstrahlung) radiation. This can be a disadvantage because it is often difficult to discriminate between the relevant spectral emissions and the broadband background emissions.
Some attempts have been made with previous laser induced breakdown spectroscopy (LIBS) devices to deal with this problem. For example, in some LIBS devices a small, fixed delay of a few to tens of microseconds is imposed between creation of the plasma and measurement of spectral emissions. While this brief, fixed delay provides some benefits, it too has various drawbacks. For example, at relatively high energies, for example 5 J or so (which is beyond the 10-250 mJ typically used in many current LIBS applications), the excitation and relaxation processes become much more complex. Some processes can be significantly delayed. As a result neither short delays nor fixed delays are optimum in all circumstances.
Other problems with traditional spark spectroscopy devices exist. For example, another type of device uses a single electrode. This single electrode spark device has various drawbacks. For example, these single electrode devices are primarily used to analyze solid, metallic samples and have limitations on their quantitative accuracy. Additionally, electrodes used in certain devices have relatively short workable lifetimes and suffer from corrosion and problems with sputtering. In some cases, the electrode itself contains material that, potentially, can interfere with the measurement of the spectral emissions of interest. Various other drawbacks exist.
One application of SIBS is as a continuously operating air pollution monitor. Existing technologies for continuous air pollution monitoring include systems based on laser excitation or employ extractive Inductively Coupled Plasma (ICP) technology. These systems are relatively expensive. A SIBS-based continuous emission monitor (CEM) does not require the expensive laser or extraction system and can be less expensive.
Another application of SIBS is as an on site monitor. Some LIBS devices have been developed for on site analysis, however, these devices are relatively expensive and suffer other drawbacks. For example, U.S. Pat. No. 5,379,103 relates to a mobile apparatus which allows in situ measurement and data collection of ground water trace element pollutants. This LIBS system is shown as having a probe coupled to a laser through a fiber optic element and another fiber optic element is used to couple the probe to spectrum analysis equipment. The spectrum is analyzed by use of an optical multichannel analyzer, a relatively costly piece of equipment. The device in the U.S. Pat. No. 5,379,103 patent appears to focus on analyzing liquid samples. These and other drawbacks exist.